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Re: [Discuss-gnuradio] Help using simple_framer and simple_correlator
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Subject: |
Re: [Discuss-gnuradio] Help using simple_framer and simple_correlator |
Date: |
Fri, 18 Nov 2005 11:21:56 -0500 |
On Thu, 17 Nov 2005 15:41:15 -0800, Eric Blossom address@hidden
>>On Thu, Nov 17, 2005 at 04:16:55PM -0500, address@hidden
wrote:
>> I am also in the process of studying this part of the software to see if
I
>> can use it to recreate my data from the demodulated signal.
> Let me start by saying that you'd be *much* better off studying the
> packet framing / deframing and clock recovery code that is used in the
> new gmsk2.py and gmsk2_pkt.py files in
gnuradio-core/src/python/gnuradio/blksimpl
> and the corresponding examples in gnuradio-examples/python/gmsk2
> The new code is much cleaner and faster, and since it tracks symbol
> timing, works for long packets.
> As Bob pointed out, the so called GMSK receiver will receive pretty
> much any kind of FSK data.
It is brand spanking new code, I had to get a new cvs.
I did a very quick look and it is very different than the frame/correlate
code.
Will this work for very low data rate? I saw in on of the files,
digital_voice.py.real, that the frame adds 10 bytes of overhead. In my
application I am need to keep it to 1 byte. Is this possible with this
code?
> With the new code you specify the nominal samples/baud (spb), which
> needn't be an integer, and it recovers the clock, resamples the
> incoming data so that we're sampling in the middle of a bit, and then
> passes the properly timed data off to the packet sink. The packet
> sink correlates for the sync pattern in a similar fashion to
> gr_simple_correlator, but is simpler, since it's not dealing with
> oversampled data. The clock recovery code take a parameter that
> specifies the maximum relative frequency error that it will track out.
> The default value is 200 parts per million (ppm), which should be
> plenty loose for anything with a xtal oscillator in it.
> Trust me, you really want to be studying the new code...
I do trust you and this code sound real good. Any reference material that
this was based on?
>Eric
Thanks a bunch,
Mike
PS: Back to some heavy studying of this new code.
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